Neuroendocrinology of Human Scalp Hair Follicles: Growth Hormone-Releasing Hormone Stimulates Hair Growth and Controls a Fully Functional Intrafollicular Hypothalamic-Pituitary-Somatotropic Signaling Axis

The study reveals that human scalp hair follicles (HFs) produce key HPS axis neurohormones, including growth hormone (GH) and its upstream regulator, growth hormone-releasing hormone (GHRH). The research involved organ-culturing and stimulating human scalp HFs with GH and GHRH. Results showed that GHRH stimulation significantly upregulated both GH and somatostatin (SST) protein and mRNA expression in the hair matrix and outer root sheath (ORS) keratinocytes ex vivo. After 6 days of GHRH treatment, test HFs remained significantly longer in anagen (active growth phase) than vehicle-treated HFs and showed increased IGF-1 protein expression in the ORS. This suggests that GHRH is a novel endogenous modulator of human hair growth and that human scalp HFs operate a fully functional peripheral equivalent of the central HPS neuroendocrine signaling axis. This newly identified neuroendocrine system in human skin could be clinically relevant for developing new hair growth intervention strategies.